Is there a way to give the main PC priority on bandwidth?

so someones busy draining the wireless... doesnt bother me cause theres no capp.. but when im on it seems for me its very slow, ive got a 4mbps linespeed atm .. dunno what the person is doing to be makin me so slow.. so is there a way to prioritize my pc over the wireless users, like slowing them down or limiting their speeds while im on?